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Old 08-09-2011, 09:31 AM   #1
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Join Date: Aug 2003
Location: Texas
Posts: 4,039
Default want to use solar panel to power led light strip - conversion help needed

I'm looking to run an LED light strip along the inside of my raised garden. I'm currently using a solar LED light set, but it gives off way too little light.

I was checking out these - http://www.coolerguys.com/840556094821.html

Voltage: 12v DC
Power: 24W
Current: 2A

I'd like to power it via a set of batteries recharged by a solar panel. I don't need the maximum brightness - as a matter of fact, I have a strip of non-waterproof LEDs that are way too bright.

Ideally, I'd need to run 2 sets of strips - either inline or powered separately.

Can someone help me out on what I'd need as far as a panel and battery pack?
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Old 08-09-2011, 10:56 AM   #2
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Join Date: Apr 2002
Location: Columbus of Ohio
Posts: 24,053

It will be hard to find a solar panel/battery pack solution that can run those for very long.
24W and 2A is a lot of power for a small, cheap solar panel/battery pack.
What is your budget? It might be over $100 for a solar panel/battery pack.

That string is essentially 100 parallel strings of 3 LEDs each.
Each set of 3 LEDs requires ~12v (probably only 9-10v) and has a ~20mA drive current.
Each set of 3 has a current limiting resistor, so all you need to do is supply voltage and it will draw its own current requirements.
If you cut 3 LEDs off, the 2A drive current will reduce by 1% (1/100).

How long are you wanting to run the lights after they are fully charged?
To run them at full brightness, you need to find a 12v 2000 mAh battery and it will power the string for 1 hour.
(Half the battery capacity of 1000mAh would give roughly half brightness and double runtime)

Last edited by edro; 08-09-2011 at 12:01 PM.
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Old 08-10-2011, 02:22 PM   #3
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Location: North Carolina
Posts: 16,237

It isn't going to be anywhere as cheap as just plugging them in but if you need solar, read on.
As said for every hour you run the lamps you need 2A from the battery. If you run it for 8 hours you need a 16AH rated battery.
A panel that can charge that will need to be rated at about 30 watts because solar panels are not 100%.

Something like this for the panel and charger



Last edited by Modelworks; 08-10-2011 at 02:24 PM.
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Old 08-10-2011, 02:35 PM   #4
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Posts: 11,212

no need to run it if nobody's there right? i'd rig up a motion detector to turn the array on. that would cut the size/cost of the battery + panel.
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Old 08-10-2011, 03:59 PM   #5
William Gaatjes
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Join Date: May 2008
Location: s orbital
Posts: 13,310

If you do not need the full brightness, you can save on the power consumed by the led strip as well by using a switching regulator. Switching regulators have a very high efficiency if properly designed. For example some experiment i did at work, i noticed that with a certain led the rated current was 700 mA. when i went back to 500mA, less light of course but not that much of a reduction as i expected it to be.

12V * 0.7A = 8.4W.
12V * 0.5A = 6 W.
Thus a consumption reduction of 2.4W i managed without a large loss of light.

Also reflectors can make up for the reduction in output power if you need a small bundle of light instead of illuminating a large area. You can win a lot with a proper design.
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